在我的Spring Boot / Data / JPA / QueryDSL应用程序中，我有以下实体：
@Entity
@NamedEntityGraph(name = "graph.User", attributeNodes = { @NamedAttributeNode("authorities") })
@Table(name = "users")
public class User extends BaseEntity implements UserDetails {
private static final long serialVersionUID = 8884184875433252086L;
@Id
@SequenceGenerator(name = "users_id_seq", sequenceName = "users_id_seq", allocationSize = 1)
@GeneratedValue(strategy = GenerationType.AUTO, generator = "users_id_seq")
private Long id;
private String username;
....
@JsonIgnore
@ManyToMany(fetch = FetchType.EAGER)
@JoinTable(name = "users_authorities", joinColumns = { @JoinColumn(name = "user_id") }, inverseJoinColumns = { @JoinColumn(name = "authority_id") })
private Set<Authority> authorities = new HashSet<Authority>();
....
}
@Entity
@Table(name = "authorities")
public class Authority implements GrantedAuthority {
private static final long serialVersionUID = 6118293571787931020L;
@Id
@SequenceGenerator(name = "authorities_id_seq", sequenceName = "authorities_id_seq", allocationSize = 1)
@GeneratedValue(strategy = GenerationType.AUTO, generator = "authorities_id_seq")
private Integer id;
@NotEmpty
private String name;
@ManyToMany(fetch = FetchType.LAZY, mappedBy = "authorities")
private Set<User> users = new HashSet<User>();
....
}
以及以下load方法：
@Override
public List<User> load(int first, int pageSize, String sortField, SortOrder sortOrder, Map<String, Object> filters) {
PageRequest pageRequest = null;
Page<User> page;
int pageIndex = first / pageSize;
if (sortField == null || sortField.isEmpty()) {
pageRequest = new PageRequest(pageIndex, pageSize);
} else {
Sort.Direction direction = sortOrder == SortOrder.ASCENDING ? Sort.Direction.ASC : Sort.Direction.DESC;
pageRequest = new PageRequest(pageIndex, pageSize, new Sort(direction, sortField));
}
Predicate predicate = UserExpressions.lazyPredicate(filters);
page = userService.findAll(predicate, pageRequest);
....
}
在此方法调用之后，我看到以下调试信息：
Hibernate: select count(user0_.id) as col_0_0_ from users user0_ where user0_.id is not null
1266079 WARN o.h.h.i.ast.QueryTranslatorImpl - HHH000104: firstResult/maxResults specified with collection fetch; applying in memory!
Hibernate: select user0_.id as id1_10_0_, authority2_.id as id1_0_1_, user0_.created_date as created_2_10_0_, user0_.updated_date as updated_3_10_0_, user0_.account_non_locked as account_4_10_0_, user0_.age as age5_10_0_, user0_.birthday as birthday6_10_0_, user0_.email as email7_10_0_, user0_.enabled as enabled8_10_0_, user0_.first_name as first_na9_10_0_, user0_.gender as gender10_10_0_, user0_.last_name as last_na11_10_0_, user0_.password as passwor12_10_0_, user0_.username as usernam13_10_0_, authority2_.name as name2_0_1_, authoritie1_.user_id as user_id1_10_0__, authoritie1_.authority_id as authorit2_11_0__ from users user0_ left outer join users_authorities authoritie1_ on user0_.id=authoritie1_.user_id left outer join authorities authority2_ on authoritie1_.authority_id=authority2_.id where user0_.id is not null
正如您所看到的，根据"WARN o.h.h.i.ast.QueryTranslatorImpl - HHH000104: firstResult/maxResults specified with collection fetch; applying in memory!" - 分页应用于内存中，在数千条记录的情况下，这种分页是不完全可以接受的。
如何更改我的配置以便在数据库级别应用分页？